Synthetic ester lubricants



States Patent?) 2,798,083 Ice Patented July 2, 1957 SYNTHETIC ESTERLUBRICANTS No Drawing. Application February 3, 1954, Serial No. 408,016

3 Claims. (Cl. 260-4106) This invention relates to synthetic esterlubricants and their preparation and is particularly concerned with thediesters of substituted propanediols.

The hydrocarbon lubricating oils are widely used but suiter from certaindisadvantages which limit their use for certain applications. Inparticular, hydrocarbon oils undergo marked viscosity changes withchanges in tem-' perature and have relatively high pour points when theyhave a usable viscosity at high temperatures. Furthermore, thehydrocarbon oils suitor oxidation or other thermal decomposition at hightemperatures. When hydrocarbon lubricating oils having a low pour pointare used, they usually contain a considerable amount of volatilematerial which is lost at high temperatures and thus greatly affects thelubricating power of the oil.

Because of these inherent disadvantages, the hydrocarbon lubricatingoils are not suitable for use in such critical applications aslubrication of turbo-jet aircraft engines and aircraft instruments. Inrecent years, a number of synthetic lubricants have been proposed toovercome some or all of these disadvantages. In general these syntheticlubricating oils are of ester type and they are characterized by lowerchanges in viscosity with changing temperature, low pour point, highoxidative stability and low volatility.

It is an object of this invention to provide a new class of syntheticester lubricants which are not subject to many of the disadvantagesinherent in hydrocarbon lubricating oils.

It is another object of this invention to provide a new method formaking synthetic lubricating oils which were not known heretofore.

Another object of this invention is to provide a highly efiective groupof new compounds which have a low viscosity slope, a low pour point, ahigh oxidative stability I and low volatility.

Another object of the invention is to provide hitherto unknown diestersof 2,2 dimethyl 3 isopropyl 1,3 propanediols which have particularutility as synthetic lubricants.

Other object will be apparent from the description and claims whichfollow.

These and other objects are attained by means of this invention asdescribed in detail hereinafter with particular reference to certainpreferred embodiments thereof. The

compounds embodying this invention are synthetic lubricants comprisingacyl diesters of the formula:

wherein each R is a straight or branched chain alkyl or alkoxy alkylgroup at least one of which contains at least 8 carbon atoms, and R iseither hydrogen or a lower alkyl radical. The simple diesters embodyingthe invention are prepared by reacting one molar proportion of apropanediol of the formula:

with 2 molar proportions of a monocarboxylic acid of the.

formula:

RCOOH wherein R is a straight or branched chain alkyl or alkyl alkoxygroup containing at least 8 carbon atoms. The

esters thus. obtained are characterized by having a lowis reacted with amonocarboxylic acid containing at least 9 carbon atoms in order to fullyesterify the diol. Another typical lubricant embodying the invention .isprepared by reacting 2,2-dimethyl-3-isopropyl-1,3-propanediol with amonocarboxylic acid of the same type. In practicing the invention, themonocarboxylie acid can be any acid of the formula:

wherein R is a straight or branched chain alkyl or alkoxy alkyl groupcontaining at least 8 carbon atoms. The acids employed are thusaliphatic acids, and can be fatty acids of the acetic acid series orbranched chain derivatives. thereof or they can be acids which containan ether linkage inthe chain. A particularly suitable group of acids arethe branched chain 0x0 acids which are prepared by the reaction ofcarbon monoxide and hydrogen on the olefins obtainable from petroleumand oxidation of the resulting aldehydes. These oxo acids have a highlybranched structure and are derived from such materials as propylenetrimers, propylene tetramers, isobutylene trimers, isobutylene.tetramers, the C7 olefins and similar well known olefins. Thus, forexample, suitable acids are fatty acids such as pelargonic acid, lauricacid,

myristic acid, palmitic acid, stearic acid and the like; and thebranched-chain 0x0 acids such as decylic acid derived from propylenetrimers, tridecylic acid derived from propylene tetramer or fromisobutylene trimer, or 'similar well known branched chain 0x0 acids, aswell as any of the other well known aliphatic acids containing at least9 carbon atoms. Similarly, the alkoxy alkyl acids containing at least 9carbon atoms are also suitable. In the case of the mixed estersdescribed hereinafter, such acids can be used with a lower acidcontaining as low as 6 carbon atoms.

The diester lubricants embodying this invention can be used alone,particularly in applications where it is undesirable to employ additiveswhich would leave a residue or which might decompose or be volatile atelevated temperatures. to employ propanediol esters as defined herein inconjunction with such additives as antioxidants, anticorrosion agents,pour point depressors, viscosity improvers, or extreme pressureadditives. The synthetic lubricants embodying the invention can also beused in the formulation of greases by the usual methods, as well asbeing used in admixture with a hydrocarbon lubricating oil, anothersynthetic ester lubricant, mineral oil, or any of the other well knownlubricating materials.

By varying the nature of the acid used to esterify the diol, a varietyof products having a wide range of viscosity and pour points can beobtained. In most cases, the acid employed will contain from 10 to about22 carbon atoms although the synthetic fatty acids having chain. lengthsof as much as 30 carbon atoms. or more can be used in some cases,particularly where a low pour point is not necessary.

These lubricants are readily prepared by heating 2 molar equivalents ofthe desired acid as defined herein with one molar equivalent of thepropanediol of. the formula:

The conditions under which the esterification is effected can be variedin accordance with well-known practice for effecting esterification ofan alcohol with an acid. In most cases, it is desirable to heat themixture of the acid and the propanediol to a temperature of about150-200 C. for a time sufficient to cause evolution of 2' molarequivalents of water. If desired this water can be removed as formed,but this is not necessary in practicing the invention. When the water isremoved, an entraining solvent such as xylene or Stoddard solvent can beused or the water can be distilled off without the use of a solvent.When esterification is substantially complete, the diesters obtained arewashed with an alkaline material to remove unreacted acid and are thendistilled at reduced pressure.

The viscosity and pour point characteristics of the diesters embodyingthis invention are illustrated in Table I for typical synthetic esterlubricants prepared as described herein and a comparison is made withthe properties of a typical hydrocarbon oil. out in the table wasdetermined by ASTM method D-88 44 and the pour point data by amodification of ASTM method D-97-47.

Table I Kinematic Viscosity in Centistokes Pour Lubricant Point,

F. 100 F. 210 F.

Typical hydrocarbon oil l3. 2. 6 -30 2,2,4-Trimethyl-l,3-pentancdiol dicaprate 13. 2 3. 0 65 2,2-Din1ethylpropanedlo1 dipelargonate 7. 8 2. 3below 85 The caprate" diester set out in the table was the ester of theC acid derived from propylene trimer by oxida: tion of the correspondingoxo aldehyde and is a branched chain corresponding in chemicalcomposition to the caprate diester. As can be seen from the table, thelubricants prepared by means of this invention have excellent viscosityand pour point characteristics.

'A particularly useful class of synthetic lubricants is prepared byesterifying a propanediol as defined herein with a mixture of two ormore acids. The acids employed can be mixtures of straight and branchedchain The viscosity data set In some cases, however, it may be desirableI acids, mixtures of acids having the same number of car atoms in themolecule provided that at least one of such acids and preferably bothacids contain at least 9 carbon atoms. Similarly, the lubricantsembodying this invention can be mere mechanical mixtures of two or moreesters as described herein. In most cases, however, the mixed estersprepared by esterifying one molar proportion of the propanediol with twomolar proportions of a mixture of acids are preferred.

By the use of mixtures of acids with one or more of the propanediols asherein defined, the pour points and viscosity characteristics of thediesters can be made in any predetermined range. Thus, for example, if2,2-dimethyl-1,3-propanediol is esterified with a mixture of three acidsRICOOH, RzCOOH- and RsCGOH wherein each R is an alkyl group of at least8 carbon'atoms, the resulting mixed product will contain the followingesters: Similar mixtures are obtained using the propanediol, 2,2-

Similar mixtures are obtained using the propanediol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, and the number of ester componentsis doubled when a mixture of propanediols is employed.

It is often desirable to be able to prepare a lubricant with aparticular set of values for the pour point and viscositycharacteristics. Thus, for example, lubricants for use in aircraftinstruments should be light lubricants having viscosities in the rangeof 48 centistokes at F., whereas the medium lubricants havingviscosities in the range of 10-15 centistokes at 100 F. are useful inturbojet engines, and the heavy lubricants having viscosities of 15-25centistokes at 100 F. are useful for high temperature applications.

Typical examples of synthetic dicster lubricants prepared by reactingtypical propanediols with mixtures of acids having the same number ofcarbon atoms in the molecule are set out in Table II:

The decanoate diesters set out in Table II were prepared by esterifyingthe respective diols with a mixture of C10 branched chain acids, andtridecanoate diesters were prepared by esterifying the respective diolswith a ture of C13 branched chain acids.

Another highly useful group of lubricants are those prepared byesterifying a propanediol with a mixture of acids having diflerentnumbers of carbon atoms but in which at least one of the acids contains9 carbon atoms. Typical examples of these lubricants are set out inTable III. Mixed ester A was prepared by esterifying2,2-dimethyl-1,3-propanediol with a mixture of equal parts by weight ofa branched chain iso-octanoic acid mixture and a mixture of. branchedchain decanoic acids. Mixed ester B was prepared by esterifying the samepropanediol with a mixture of equal parts by weight of Z-ethyl hexanoicacid, a mixture of branched chain decanoic acids, and a mixture ofbranched chain tridecanoic acids. Mixed ester C was prepared byesterifying 2,2-dimethyl-3-isopropyl- 1,3-propanediol with a mixture ofequal parts by Weight of Z-ethylhexoic acid, a mixture of branched chainisooctanoic acids, and a mixture of branched chain decanoic acids.

The diester lubricants embodying this invention are characterized by ahigh degree of thermal stability and resistance to oxidation. Thus, theester compositions as described herein can be refluxed at atmosphericpressure for 24 hours at a pot temperature of 335 C. and in the presenceof air. After this prolonged heating period, the weight loss is usuallyless than about 1.0% which indicates the low content of volatilematerial in the diester and its chemical stability, since very little ofthe lubricant is decomposed to volatile decomposition products.Furthermore, the color of the lubricant is substantially unchangedfollowing this test and there is no free acid present.

Thus, by means of this invention, a highly useful class of syntheticdiester lubricants is provided. The improved physical characteristicsmake these materials eminently suitable for use as lubricating oils inthe applications Where hydrocarbon lubricating oils are now used, andparticularly in high temperature applications where hydrocarbonlubricating oils are completely unsuitable. Because of their low pourpoint and high oxidative and thermal stability, it is usually notnecessary to employ additives with these diester lubricants which meansthat they can be used very successfully in jet aircraft and similarapplications where the presence of a residue is undesirable. Thestraight chain fatty acid diesters are completely suitable, but thebranched chain diesters are preferably prepared due to the modificationof the physical properties by the presence of the branched chain. Theeffect of the branched chain is particularly noticeable in the viscositycharacteristics of the product. Thus, the branched chain diestersprepared by use of the oxo acids remain fluid for higher molecularweights than is the case with the straight chain diesters. The mixedesters are particularly desirable because they can be prepared to anydesired characteristics.

The invention has been described in considerable detail with particularreference to certain preferred embodiments thereof but it will beunderstood that variations and modifications can be elfected within thespirit and scope of the invention as described hereinabove and asdefined in the appended claims.

We claim:

1. A synthetic lubricant comprising a diester of the formula O OH:CH-CHs O wherein each R is a member of the group consisting of straightand branched chain alkyl groups, one R containing 421 carbon atoms andthe other R containing 82l carbon atoms.

2. A synthetic lubricant comprising an acyl diester of2,2-dimethyl-3-isopropyl-1,3-propanedio1 wherein each acyl groupcontains 921 carbon atoms.

3. A synthetic lubricant comprising 2,2-dimethyl-3-isopropyl-1,3-propanediol dipelargonate.

References Cited in the file of this patent UNITED STATES PATENTS2,492,955 Ballard et al. Jan. 3, 1950 2,499,983 Beavers Mar. 7, 19502,520,733 Morris et al. Aug. 29, 1950 2,563,609 Mutuszak Aug. 7, 19512,705,724 Cottle Apr. 5, 1955 OTHER REFERENCES Oil and Gas Journal, 51,No. 43 (1953), pages 74-77.

Petroleum (London), 17, No. 147 (1954), pages 122-126.

Ind. and Eng. Chem., vol. 45, No. 8, pages 1766-1775.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,798,083 July 2, 1957 Alan Bell et al.

It is hereby certified that error appears .in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read 'as corrected below.

Column 6, line 29, fair "9-21" read 9-22 Signed and sealed this 10th dayof September 1957.,

1 meat:

KAR AXLINE ROBERT c. WATSON

1. A SYNTHETIC LUBRICANT COMPRISING A DIESTER OF THE FORMULA 